76
3. MEASURING GROWTH AND FORM
The local availability of light and the exposure to water movement are the
dominant environmental influences; sedimentation and transport of food
particles are closely related to the hydrodynamic parameter. Typicalexamples
of this morphological plasticity and the relation to the physical environment
are: Fig. 2.31 showing a range of growth forms of the scleractinian Montastrea
annularis and local light intensities (Barnes 1973, Graus and Macintyre 1982);
growth forms of the hydrozoan Millepora spp. and exposure to water movement (Stearn and Riding 1973> de Weerdt 1981); the variations in morphology
due to differences in exposure to water movement in the scleractinian Pocillopora damicornis shown in Fig. 1.1 (see also Lesser et al. 1994), Madracis
mirabilis (see Fig. 2.5 and Sebens et al. 1997), and Agaricia agaricites (Helmuth and Sebens 1993); the shape of coralline algae (see Fig. 1.3dand e) and
the effect of exposure to water movement (Bosence 1976); and the growth
forms of the sponge Haliclona oculata shown in Fig. 2.16 (Kaandorp 1991,
Kaandorp and de Kluijver 1992)and the exposure to water movement.
Since the physical environment has a strong impact on the growth
process, distinct growth forms of marine sessile organisms can often be associated with an environmental gradient, where the amount of water movement
is usually the most dominant parameter. In Veron and Pichon (1976) several
series of growth forms of scleractinians (for example Pocillopora damicornis
and Seriatopora hysterix) are presented, which are arranged along a gradient
of the amount of water movement. Among studied specimens of both scleractinians the growth forms showed a gradual transformation from a compact
shape, under exposed conditions, to a thin-branching shape under sheltered
conditions. In Fig. 1.1 a range of growth forms of P. damicornis are shown.
Form (a) originated from the most exposed site, form (f) originated from
the most sheltered site, and in the range (a) to (f) the exposure to water
movement gradually decreases. In the growth forms of the sponge Haliclona
oculata shown in Fig. 2.16 a plate-like, more compact shape was found at exposed sites; this shape was gradually replaced by a thin -branching form at
less exposed sites (Kaandorp 1991, 1994b). A similar trend was observed in
growth forms of the hydrozoan Millepora alcicornis (de Weerdt 1981). In this
species the shape changed from plate-like forms at shallow and exposed sites
to thin-branching forms at deeper and sheltered locations.
In this section a range of growth forms for each of three species - the
sponge Haliclona oculata,the scleractinian coral Pocillopora damicornis,and
the hydrozoan Millepora alcicornis - was morphologically analyzed. Samples
of the species were collected along a gradient of exposure to water movement.
The idea was that by analyzing growth forms from very different taxonomical groups, it might be possible to identify some generic effects of the impact
of water movement on the overall growth form of organisms with accretive growth , and to distinguish these from species-specific morphological
features, which are presumably controlled by genetic regulation (Kaandorp
1999). An example of a morphological feature which might be regulated
by biological mechanism is the average distance between branch tips and
neighboring branches ("branch spacing"). In studies on particle capture in
the branching scleractinian Madracis mirabilis(see Fig. 2.5) and the influence
of hydrodynamics (see also Sect. 2.1.1 and Sebens et al. 1997), it was demonstrated that branch spacing is a crucial morphological property. Branch
spacing is variable and may be controlled by a chemical agent (see Sect. 2.2.4
and Rinkevich and Loya1985a). Sebens et al. (1997) argue that through modi-
3. MEASURING GROWTH AND FORM
The local availability of light and the exposure to water movement are the
dominant environmental influences; sedimentation and transport of food
particles are closely related to the hydrodynamic parameter. Typicalexamples
of this morphological plasticity and the relation to the physical environment
are: Fig. 2.31 showing a range of growth forms of the scleractinian Montastrea
annularis and local light intensities (Barnes 1973, Graus and Macintyre 1982);
growth forms of the hydrozoan Millepora spp. and exposure to water movement (Stearn and Riding 1973> de Weerdt 1981); the variations in morphology
due to differences in exposure to water movement in the scleractinian Pocillopora damicornis shown in Fig. 1.1 (see also Lesser et al. 1994), Madracis
mirabilis (see Fig. 2.5 and Sebens et al. 1997), and Agaricia agaricites (Helmuth and Sebens 1993); the shape of coralline algae (see Fig. 1.3dand e) and
the effect of exposure to water movement (Bosence 1976); and the growth
forms of the sponge Haliclona oculata shown in Fig. 2.16 (Kaandorp 1991,
Kaandorp and de Kluijver 1992)and the exposure to water movement.
Since the physical environment has a strong impact on the growth
process, distinct growth forms of marine sessile organisms can often be associated with an environmental gradient, where the amount of water movement
is usually the most dominant parameter. In Veron and Pichon (1976) several
series of growth forms of scleractinians (for example Pocillopora damicornis
and Seriatopora hysterix) are presented, which are arranged along a gradient
of the amount of water movement. Among studied specimens of both scleractinians the growth forms showed a gradual transformation from a compact
shape, under exposed conditions, to a thin-branching shape under sheltered
conditions. In Fig. 1.1 a range of growth forms of P. damicornis are shown.
Form (a) originated from the most exposed site, form (f) originated from
the most sheltered site, and in the range (a) to (f) the exposure to water
movement gradually decreases. In the growth forms of the sponge Haliclona
oculata shown in Fig. 2.16 a plate-like, more compact shape was found at exposed sites; this shape was gradually replaced by a thin -branching form at
less exposed sites (Kaandorp 1991, 1994b). A similar trend was observed in
growth forms of the hydrozoan Millepora alcicornis (de Weerdt 1981). In this
species the shape changed from plate-like forms at shallow and exposed sites
to thin-branching forms at deeper and sheltered locations.
In this section a range of growth forms for each of three species - the
sponge Haliclona oculata,the scleractinian coral Pocillopora damicornis,and
the hydrozoan Millepora alcicornis - was morphologically analyzed. Samples
of the species were collected along a gradient of exposure to water movement.
The idea was that by analyzing growth forms from very different taxonomical groups, it might be possible to identify some generic effects of the impact
of water movement on the overall growth form of organisms with accretive growth , and to distinguish these from species-specific morphological
features, which are presumably controlled by genetic regulation (Kaandorp
1999). An example of a morphological feature which might be regulated
by biological mechanism is the average distance between branch tips and
neighboring branches ("branch spacing"). In studies on particle capture in
the branching scleractinian Madracis mirabilis(see Fig. 2.5) and the influence
of hydrodynamics (see also Sect. 2.1.1 and Sebens et al. 1997), it was demonstrated that branch spacing is a crucial morphological property. Branch
spacing is variable and may be controlled by a chemical agent (see Sect. 2.2.4
and Rinkevich and Loya1985a). Sebens et al. (1997) argue that through modi-